Alkylating agents are broadly used as active pharmaceutical ingredients (APIs), agrochemicals, in industrial and laboratory settings, and also as chemical warfare agents. Alkylating agents can be highly mutagenic and/or carcinogenic because they form covalent bonds with endogenous compounds like DNA, proteins and other nucleophilic biomolecules. While alkylating agents have the potential to be toxic, the covalent modification of biomolecules can be a powerful treatment for a wide variety of maladies, from headaches to cancer.
Some chemotherapy drugs are very powerful alkylating agents. Nevertheless, the curative properties of chemotherapy drugs outweigh their carcinogenicity and mutagenicity for many cancer patients. However, exposure to non-patients is unacceptable. The highest risk groups are healthcare workers who may be chronically exposed to antineoplastic drugs throughout the course of their duties. Occupational exposure to chemotherapy drugs leads to skin rashes, liver toxicity, adverse reproductive outcomes, leukemia and cancer. In 2004, the National Institute for Occupational Safety and Health (NIOSH) reported that the number of exposed healthcare workers may exceed 5.5 million in the United States, and from this statistic it may be estimated that over half a million workers in Canada may be similarly compromised. Current cleaning protocols for antineoplastic drug spills may result in spreading the contamination over a larger area rather than cleaning of the spill.
4-(4-nitrobenzyl)pyridine or NBP (CAS No. 1083-48-3) is commonly used in testing for alkylating agents as a colorimetric indicator compound. NBP is used in toxicology screening of pharmaceutical compounds, detection of chemical warfare agents, environmental hygiene technology, and in other chemical analyses. The use in determining toxicology profiles and mutagenicity of medicinal compounds is due to NBP's reactive similarity to guanine.
NBP was first applied towards the detection of mustard gas agents by the Koenigs et al in 1925 (Koenigs, E., Kohler, K., and Blindow, K. Ber. Dtsch. Chem. Ges. 1925 58, 933-940). Later, Epstein increased the NBP method's accuracy and used it for quantitative determinations, and so often NBP is referred to as the “Epstein reagent” (Epstein, J.; Rosenthal, R. W.; Ess, R. J. Anal. Chem. 1955, 27, 1435-1439). The suggested mechanism follows an SN2 displacement of a halide by the nucleophilic pyridine, as shown from conversion from I to II in acetone/water. Upon addition of base like triethylamine or NaOH, one of the acidic methylene protons is removed, effectively yielding the carbanion III (Dierickx, K.; et al. Talanta 2009, 77, 1370-1375).